The present invention relates to a display apparatus of a plasma display panel (PDP) and digital micromirror device (DMD), and more specifically, to a display apparatus capable of adjusting a subfield number in accordance with brightness.
A display apparatus of a PDP and a DMD makes use of a subfield method, which has binary memory, and which displays a dynamic image possessing half tones by temporally superimposing a plurality of binary images that have each been weighted. The following explanation deals with PDP, but applies equally to DMD as well.
A PDP subfield method is explained using FIGS. 1; 2, and 3.
Now, consider a PDP with pixels lined up 10 across and 4 vertically, as shown in FIG. 3. Let the respective R, G, B of each pixel be 8 bits, assume that the brightness thereof is rendered, and that a brightness rendering of 256 gradations (256 gray scales) is possible. The following explanation, unless otherwise stated, deals with a G signal, but the explanation applies equally to R, B as well.
The portion indicated by A in FIG. 3 has a signal level of brightness of 128. If this is displayed in binary, a (1000 0000) signal level is added to each pixel in the portion indicated by A. Similarly, the portion indicated by B has a brightness of 127, and a (0111 1111) signal level is added to each pixel. The portion indicated by C has a brightness of 126, and a (0111 1110) signal level is added to each pixel. The portion indicated by D has a brightness of 125, and a (0111 1101) signal level is added to each pixel. The portion indicated by E has a brightness of 0, and a (0000 0000) signal level is added to each pixel. Lining up an 8-bit signal for each pixel perpendicularly in the location of each pixel, and horizontally slicing it bit-by-bit produces a subfield. That is, in an image display method, which utilizes the so-called subfield method, by which 1 field is divided into a plurality of differently weighted binary images, and displayed by temporally superimposing these binary images, a subfield is 1 of the divided binary images.
Since each pixel is displayed using 8 bits, as shown in FIG. 2, 8 subfields can be achieved. Collect the least significant bit of the 8-bit signal of each pixel, line them up in a 10xc3x974 matrix, and let that be subfield SF1 (FIG. 2). Collect the second bit from the least significant bit, line them up similarly into a matrix, and let this be subfield SF2. Doing this creates subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8. Needless to say, subfield SF8 is formed by collecting and lining up the most significant bits.
FIG. 4 shows the standard form of a 1 field PDP driving signal. As shown in FIG. 4, there are 8 subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 in the standard form of a PDP driving signal, and subfields SF1 through SF8 are processed in order, and all processing is performed within 1 field time.
The processing of each subfield is explained using FIG. 4. The processing of each subfield constitutes setup period P1, write period P2 and sustain period P3. At setup period P1, a single pulse is applied to a sustaining electrode, and a single pulse is also applied to each scanning electrode (There are only up to 4 scanning electrodes indicated in FIG. 4 because there are only 4 scanning lines shown in the example in FIG. 3, but in reality, there are a plurality of scanning electrodes, 480, for example.). In accordance with this, preliminary discharge is performed.
At write period P2, a horizontal-direction scanning electrodes scans sequentially, and a predetermined write is performed only to a pixel that received a pulse from a data electrode. For example, when processing subfield SF1, a write is performed for a pixel represented by xe2x80x9c1xe2x80x9d in subfield SF1 depicted in FIG. 2, and a write is not performed for a pixel represented by xe2x80x9c0.xe2x80x9d
At sustain period P3, a sustaining pulse (driving pulse) is outputted in accordance with the weighted value of each subfield. For a written pixel represented by xe2x80x9c1,xe2x80x9d a plasma discharge is performed for each sustaining pulse, and the brightness of a predetermined pixel is achieved with one plasma discharge. In subfield SF1, since weighting is xe2x80x9c1,xe2x80x9d a brightness level of xe2x80x9c1xe2x80x9d is achieved. In subfield SF2, since weighting is xe2x80x9c2,xe2x80x9d a brightness level of xe2x80x9c2xe2x80x9d is achieved. That is, write period P2 is the time when a pixel which is to emit light is selected, and sustain period P3 is the time when light is emitted a number of times that accords with the weighting quantity.
As shown in FIG. 4, subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 are weighted at 1, 2, 4, 8, 16, 32, 64, 128, respectively. Therefore, the brightness level of each pixel can be adjusted using 256 gradations, from 0 to 255.
In the B region of FIG. 3, light is emitted in subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, but light is not emitted in subfield SF8. Therefore, a brightness level of xe2x80x9c127xe2x80x9d (=1+2+4+8+16+32+64) is achieved.
And in the A region of FIG. 3, light is not emitted in subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, but light is emitted in subfield SF8. Therefore, a brightness level of xe2x80x9c128xe2x80x9d is achieved.
With the PDP subfield method explained above, to provide an optimum screen display in bright places and dark places, it is necessary to make adjustment in accordance with the brightness of an image.
A PDP display apparatus capable of brightness control is disclosed in the specification of Kokai No. (1996)-286636 (corresponds to specification in U.S. Pat. No. 5,757,343), but here, only light emission frequency and gain control are performed in accordance with brightness, making adequate adjustment impossible.
An object of the present invention is to provide a display apparatus capable of adjusting a subfield number in accordance with brightness, designed to be able to adjust the number of subfields in accordance with the brightness of an image (comprising both a dynamic image and a static image). The average level of brightness, peak level, PDP power consumption, panel temperature, contrast and other factors are used as parameters that represent image brightness.
By increasing the subfield number, it is possible to eliminate pseudo-contour noise, which is explained below, and conversely, by decreasing the subfield number, although there is the likelihood that pseudo-contour noise will occur, it is possible to produce a clearer image.
Pseudo-contour noise is explained below.
Assume that regions A, B, C, D from the state shown in FIG. 3 have been moved 1 pixel width to the right as shown in FIG. 5. Thereupon, the viewpoint of the eye of a person looking at the screen also moves to the right so as to follow regions A, B, C, D. Thereupon, 3 vertical pixels in region B (the B1 portion of FIG. 3) will replace 3 vertical pixels in region A (A1 portion of FIG. 5) after 1 field. Then, at the point in time when the displayed image changes from FIG. 3 to FIG. 5, the eye of a human being is cognizant of region B1, which takes the form of a logical product (AND) of B1 region data (01111111) and A1 region data (10000000), that is (00000000). That is, the B1 region is not displayed at the original 127 level of brightness, but rather, is displayed at a brightness level of 0. Thereupon, an apparent dark borderline appears in region B1. If an apparent change from xe2x80x9c1xe2x80x9d to xe2x80x9c0xe2x80x9d is applied to an upper bit like this, an apparent dark borderline appears.
Conversely, when an image changes from FIG. 5 to FIG. 3, at the point in time when it changes to FIG. 3, a viewer is cognizant of region A1, which takes the form of a logical sum (OR) of A1 region data (10000000) and B1 region data (01111111), that is (11111111). That is, the most significant bit is forcibly changed from xe2x80x9c0xe2x80x9d to xe2x80x9c1,xe2x80x9d and in accordance with this, the A1 region is not displayed at the original 128 level of brightness, but rather, is displayed at a roughly 2-fold brightness level of 255. Thereupon, an apparent bright borderline appears in region A1. If an apparent change from xe2x80x9c0xe2x80x9d to xe2x80x9c1xe2x80x9d is applied to an upper bit like this, an apparent bright borderline appears.
In the case of a dynamic image only, a borderline such as this that appears on a screen is called pseudo-contour noise (xe2x80x9cpseudo-contour noise seen in a pulse width modulated motion picture displayxe2x80x9d: Television Society Technical Report, Vol. 19, No. 2, IDY95-21 pp. 61-66), causing degradation of image quality.
According to the present invention, a display apparatus creates Z subfields from a first to a Zth. The display apparatus brightens or darkens the overall image by amplifying a picture signal using a multiplication factor A. The display apparatus performs weighting for each subfield, outputs a drive pulse of a number N-times this weighting, or outputs a drive pulse of a time length N-times this weighting, and adjusts brightness in accordance with the total drive pulse number in each pixel, or the total drive pulse time. In the picture signal, the brightness of each pixel is expressed by Z bits to indicate a particular gradation of the total gradations K. The first subfield is formed by collecting the 0 and 1 from the entire screen only a first bit of Z bits. The second subfield is formed by collecting the 0 and 1 from the entire screen only a second bit of Z bits. In this manner a first to a Zth subfields are formed. The display apparatus adjusts the subfield number in accordance with brightness. To this end, according to the present invention, the display apparatus comprises brightness detecting means, which acquire image brightness data; and adjusting means, which adjust the subfield number Z based on brightness data.
According to the present invention, a display apparatus creates, for each picture, Z subfields from a first to a Zth in accordance with Z bit representation of each pixel, weighting N to each subfield, a multiplication factor A for amplifying a picture signal, and a number of gradation display points K, said display apparatus comprises:
brightness detecting means, which acquire image brightness data; and
adjusting means, which adjust the subfield number Z based on brightness data.
According to a preferred embodiment, said brightness detecting means comprises average level detecting means, which detects an average level (Lav) of image brightness.
According to a preferred embodiment, said brightness detecting means comprises peak level detecting means, which detects a peak level (Lpk) of image brightness.
According to a preferred embodiment, said brightness detecting means comprises power consumption detecting means, which detects the power consumption of a display panel on which an image is depicted.
According to a preferred embodiment, said brightness detecting means comprises panel temperature detecting means, which detects the temperature of a display panel on which an image is depicted.
According to a preferred embodiment, said brightness detecting means comprises contrast detecting means, which detects the contrast of a display panel on which an image is depicted.
According to a preferred embodiment, said brightness detecting means comprises ambient illumination detecting means, which detects the peripheral brightness of a display panel on which an image is depicted.
According to a preferred embodiment, the apparatus further comprises image characteristic determining means, which generates multiplication factor A based on brightness data, and multiplication means, which amplifies a picture signal A times based on multiplication factor A.
According to a preferred embodiment, the apparatus further comprises image characteristic determining means, which generates total number of gradations K based on brightness data, and display gradation adjusting means, which changes a picture signal to the nearest gradation level based on total number of gradations K.
According to a preferred embodiment, the apparatus further comprises image characteristic determining means, which generates the weighting N based on brightness data, and weight setting means, which multiplies N-times the weight of each subfield based on multiple N.
According to a preferred embodiment, said weight setting means is a pulse number setting means, which sets a drive pulse number.
According to a preferred embodiment, said weight setting means is a pulse width setting means, which sets a drive pulse width.
According to a preferred embodiment, the subfield number Z is reduced as the average level (Lav) of said brightness decreases.
According to a preferred embodiment, the apparatus further comprises image characteristic determining means, which generates the multiplication factor A based on brightness data, and multiplying means, which amplifies a picture signal A times based on multiplication factor A, and increases multiplication factor A as the average level (Lav) of said brightness decreases.
According to a preferred embodiment, the apparatus further comprises image characteristic determining means, which generates a weighting multiplier N based on brightness data, and increases a multiplication result of multiplication factor A and weighting multiplier N as the average level (Lav) of said brightness decreases.
According to a preferred embodiment, the apparatus further comprises image characteristic determining means, which generates a weighting multiplier N based on brightness data, and increases weighting multiplier N as the average level (Lav) of said brightness decreases.
According to a preferred embodiment, the subfield number Z is increased as said peak level (Lpk) decreases.
According to a preferred embodiment, the apparatus further comprising image characteristic determining means, which generates multiplication factor A based on brightness data, and multiplying means, which amplifies a picture signal A times based on multiplication factor A, and increases multiplication factor A as said peak level (Lpk) decreases.
According to a preferred embodiment, the apparatus further comprises image characteristic determining means, which generates a weighting multiplier N based on brightness data, and decrease weighting multiplier N as said peak level (Lpk) decreases.